The present invention relates to pulse brushless direct current electric motors.
Brushless DC motors are widely used because they are stable, reliable, efficient, and require little or no maintenance. A typical brushless motor consists of a stator structure having a plurality of electromagnets, a permanent magnet rotor, and a sensor which controls the energization of the torque-creating stator electromagnets in pulses depending on the position of the rotor. Several types of brushless motors comprising this structure have been proposed—for example, in U.S. Pat. No. 3,873,987 (1975), U.S. Pat. No. 4,374,347 (1983), and U.S. Pat. No. 4,547,714 (1985), all to Muller, U.S. Pat. No. 4,030,005 to Doemen (1977), and U.S. Pat. No. 5,095,238 to Suzuki et al. (1992). All of these motors use semiconductor sensing elements based on the Hall Effect. While Hall Effect sensors are reliable and widely used in brushless motors, they have some disadvantages. They require additional electronic components, which complicates manufacturing and increases the cost of these motors. Also, additional circuitry and Hall generators themselves consume some electrical energy therefore decreasing the total efficiency of such motors, particularly noticeable in small electric motors working on low electric currents.
Other types of brushless motors using mechanical switching means that do not consume additional energy are also known from the prior art. Henninger in U.S. Pat. No. 2,753,471 (1956) shows a constant speed DC motor utilizing a vibratible switch with complex mechanical construction. The electrical contacts in this motor are exposed, which affects its life time and reliability. Better results in improving these parameters could be achieved in motors incorporating reed switches as rotor position sensors, where internal contacts are encapsulated in a glass tube filled with protective gas.
Several attempts to utilize advantages of reed switches in brushless motors were made, for example in U.S. Pat. No. 3,297,891 to Foran (1967), U.S. Pat. No. 3,662,196 to Ruschmann (1972), U.S. Pat. No. 3,678,359 to Peterson (1972), and U.S. Pat. No. 4,475,068 to Brailsford (1984). Although these motors in general have a smaller number of electrical components, all of them suffer from several disadvantages. They use a plurality of reed switches, sometimes even placed in an array. Additional magnets or shielding disks are needed to control reed switch activation which makes these motors mechanically complex.
Brushless motors incorporating reed switches are not widely used in the industry because of the common misconception of their lower reliability as compared to semiconductor sensors that have no mechanical parts. However, reed switches may provide reliable operation with an increased life time that can be comparable to the life time of Hall Effect sensors or other wearable motor components, such as bearings, when proper measures are taken to protect reed switch internal contacts from high currents and voltage spikes. All motors using reed switches heretofore known lack such measures.
Simple replacement of the Hall Effect sensor with a reed switch in any type of known brushless motor presents technical difficulties and is not obvious for any person with ordinary skills in the art. Hall Effect sensors interact with a continuous surface of the rotor magnets and provide different electric signal in the presence of South or North poles. It is known that motors with continuous magnetization of the rotor with alternating magnetic poles have improved efficiency due to better utilization of the magnets as compared to the rotors having unmagnetized regions. However, the reed switch is equally activated by any pole, therefore with a continuously magnetized rotor surface it will stay in one state despite the changes in magnetic field direction. Thus, a separate magnetic field must interact with the reed switch preserving the main uninterrupted torque generating rotor surface. It could require an extensive redesign of the rotor. Also, the electronic circuits of present brushless motors with semiconductor sensors need to be changed to provide low voltage applied to the reed switch contacts that should be electrically separated from motor windings. Additional measures are required to limit current through the reed switch. This current needs to be lower than a Hall Effect sensor supply current to achieve higher efficiency as compared to conventional technology.